[actions] add reusable workflows

.github/workflows/node-aught.yml

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+name: 'Tests: node.js < 10'
+
+on: [pull_request, push]
+
+permissions:
+  contents: read
+
+jobs:
+  tests:
+    uses: ljharb/actions/.github/workflows/node.yml@main
+    with:
+      range: '< 10'
+      type: minors
+      command: npm run tests-only
+
+  node:
+    name: 'node < 10'
+    needs: [tests]
+    runs-on: ubuntu-latest
+    steps:
+      - run: 'echo tests completed'

.github/workflows/node-pretest.yml

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+name: 'Tests: pretest/posttest'
+
+on: [pull_request, push]
+
+permissions:
+  contents: read
+
+jobs:
+  tests:
+    uses: ljharb/actions/.github/workflows/pretest.yml@main

.github/workflows/node-tens.yml

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+name: 'Tests: node.js >= 10'
+
+on: [pull_request, push]
+
+permissions:
+  contents: read
+
+jobs:
+  tests:
+    uses: ljharb/actions/.github/workflows/node.yml@main
+    with:
+      range: '>= 10'
+      type: minors
+      command: npm run tests-only
+
+  node:
+    name: 'node >= 10'
+    needs: [tests]
+    runs-on: ubuntu-latest
+    steps:
+      - run: 'echo tests completed'

.github/workflows/rebase.yml

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+name: Automatic Rebase
+
+on: [pull_request_target]
+
+permissions:
+  contents: read
+
+jobs:
+  _:
+    permissions:
+      contents: write  # for ljharb/rebase to push code to rebase
+      pull-requests: read  # for ljharb/rebase to get info about PR
+
+    name: "Automatic Rebase"
+
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+      - uses: ljharb/rebase@master
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}

.github/workflows/require-allow-edits.yml

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+name: Require “Allow Edits”
+
+on: [pull_request_target]
+
+permissions:
+  contents: read
+
+jobs:
+  _:
+    permissions:
+      pull-requests: read  # for ljharb/require-allow-edits to check 'allow edits' on PR
+
+    name: "Require “Allow Edits”"
+
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: ljharb/require-allow-edits@main